The present invention relates to apparatus and methods for repairing manufacturing defects in flat panel display devices, such as liquid crystal display (LCD) devices.
A typical LCD includes two display panels respectively having pixel electrodes and a common electrode, and a liquid crystal layer having dielectric anisotropy interposed between the display panels. The pixel electrodes are arranged in a matrix shape, and are respectively connected to corresponding switching elements, such as thin film transistors (TFTs), such that a data voltage is sequentially applied to the pixel electrodes row by row. The common electrode is formed on the entire surface of one of the display panels, and a common voltage is applied to the common electrode. The pixel electrodes, the common electrode, and the liquid crystal layer interposed therebetween constitute a liquid crystal capacitor, and the liquid crystal capacitor forms a basic unit of a pixel in conjunction with the switching element connected thereto.
In a LCD, a voltage is applied between two electrodes so as to form an electric field in the liquid crystal layer, and the intensity of the electric field is controlled so as to adjust the transmittance of light passing through the liquid crystal layer, thereby generating a desired light image. Additionally, color filters of three primary colors, for example, red, green, and blue, are provided in the common electrode region to correspond to the pixel electrodes, thereby realizing a color display.
LCDs are subjected to many tests during their manufacture, and any defects that are found during the tests must either be repaired or the panels scrapped, resulting in expensive waste.
For example, when the display signal lines are disconnected or short-circuited, or when defective pixels exist, these may be detected through certain testing procedures. These tests include an array test, a visual inspection (VI) test, a “gross” test, a module test, and so on.
The array test is performed before a “mother” glass panel is divided into separate cells, and determines disconnection of the display signal lines by applying a selected voltage to the lines and detecting whether a corresponding output voltage is generated. The VI test is performed after the mother glass is divided into separate cells, and determines disconnection of the display signal lines by applying a selected voltage to the lines and then viewing the display panels. The gross test is performed after upper and lower display panels are combined and driving circuits have been mounted, and determines image quality and disconnection of the display signal lines by applying a selected voltage to the lines that is identical to an actual driving voltage and then viewing display states of the screen. The module test is performed after the driving circuits are mounted and polarizers have been attached to the outsides of the two display panels, and determines the optimum operation of the driving circuits.
The gross test, which is intended to simulate an actual driving situation, determines defective pixels while the entire screen is blackened. In this condition, an unusually bright or “high pixel” phenomenon, that is, a “shining” of a defective pixel may occur due to foreign substances in the liquid crystal layer or the disconnection or short-circuit of wiring lines. The bright or high pixel phenomenon can occur in most types of flat panel display devices, as well as in the above-described LCDs.
In order to repair defective pixels, such as the high pixels described above, a light-shielding film can be formed on the display panel that covers a region of the outside of the panel corresponding to the position of the high pixel using, e.g., a chemical vapor deposition method or the like. However, this repair method can be problematical in that the light from the defective pixel does not leak from the front side of a display device, but instead, from a lateral side thereof, which makes it impossible to effect a complete repair. What is needed then are apparatus and methods that enable the complete, effective repair of defective pixels of a display device during its manufacture.